Fourth seed Williams, making her debut in the Olympic singles having won the doubles with sister Venus in 2000, was leading 6-3 2-1 against Olga Govortsova of Belarus when rumbling thunder had her casting her eyes anxiously to the heavens.

Minutes later the players were dashing for cover.

After the start of play was delayed by 2-� hours in the morning, the rain returned for good just before 4:30 p.m. and play was postponed at 7:00 p.m.

Organisers are confident they can make up the backlog of matches on Monday, although showers are forecast.

Ivanovic, who will lose her world number one spot on Monday to fellow Serb Jelena Jankovic, was clearly emotional when she explained her withdrawal to reporters.

"This is one of the hardest moments of my career and one of the hardest decisions I've had to take," 20-year-old Ivanovic told a news conference at the Olympic Tennis Centre.

Ivanovic said she had not been able to practise for 10 days but had travelled to China in the hope the injury to her thumb joint would recover.

"I've tried everything to recover, laser treatment, magnetic treatment ... I've had more treatments in 10 days than I've had in my life," she said.

Blake needed little more than an hour to beat Guccione on his Olympic debut. The 28-year-old said he had been inspired by watching American swimmer Michael Phelps [Images] win gold in the 400m individual medley and break the world record.

"It was something that was special because it made me realise how many people are inspired by him, and that I'm now in the position to have that opportunity, to go out there and get a medal for my country," he said.

Fernando Gonzalez of Chile, the reigning Olympic doubles champion, made it into the second round with a 6-4, 6-4 defeat of China's Sun Peng. Fourth seed Nikolay Davydenko of Russia [Images] beat Ernests Gulbis of Latvia 6-4, 6-2.